Cook the cubed potatoes in boiling salted water until firm-tender (about 7-8 minutes) drain.
Heat oil and butter in a large oven-proof skillet over medium heat.
Add in the red pepper and green or yellow onions with oregano; saute for about 5-6 minutes, adding the garlic the last few minutes.
Add in the cooked potatoes and saute for 1 minute.
In a bowl whisk together eggs, whipping cream, salt and pepper, then pour over veggies in the skillet; reduce heat to medium-low, cover the skillet and cook until the eggs are set around the edges (about 7-8 minutes, do not over cook!).
Sprinkle the top with grated cheddar cheese.
Set the oven to broil.
Place the skillet under the broiler heat (about 4-5 inches from heat) cook until the cheese is melted and very lightly browned.
Let the frittata sit for 1 minute, then slice into 8 wedges, or as desired.